Study Explores Risk Factors for PMWS

October 5, 2005 — Adam Moeser

Adam Moeser provides the following summary of a case-control study conducted in Spain. The study evaluated risk factors associated with development of postweaning multisystemic wasting syndrome (PMWS) in the presence of pre-existing porcine circovirus type 2 (PCV2) infection. This publication appeared in the latest edition of Preventive Veterinary Medicine.

A total of 62 farms were included in this study during 2002 - 2003. The farms selected were located in northeast and eastern regions of Spain representing approximately 2/3 of pig production in Spain. Farms were selected according to their PMWS status and designated as either "cases" which were farms with clinical PMWS (n=32) and "controls" which were farms without clinical PMWS (n=30). Data was obtained via a filled-in questionnaire consisting of 191 variables including variables related to general farm characteristics, breeding and replacement practices, weaning and fattening facilities description, hygiene practices, vaccination schedule, and biosecurity. Blood samples (n=45) were obtained from each farm from sows (n=15), 12-week-old pigs (n=15), and 20-week-old pigs (n=15) for determination of the presence of antibodies for PCV2, Aujesky's disease virus, PRRSV, and porcine parvovirus. Two to three pigs per case farm were necropsied and samples of superficial and inguinal lymph nodes, tonsils and lung were obtained for detection of PCV2 by in situ hybridization and histopathology. Data were analyzed using conditional logistic regression with a nested n:m matched design stratified according to farm size.

Of the farms tested in this study, mortality rates were higher in PMWS case farms compared to control farms (6.9% vs. 2.9% in 12-week-old pigs; 7.7% vs. 4% in 20-week-old pigs). In the final statistical model, only 3 variables (vaccination of gilts against PRRSV, vaccination against atrophic rhinitis, and PCV2 seroprevalence) had a significant relationship with PMWS status. Vaccination of gilts against PRRSV increased the odds ratio (OR = 5.1) for PMWS (P<0.04) while farms that vaccinated against atrophic rhinitis had a decreased odds ratio for development of PMWS (OR = 0.19). These results should be interpreted with caution due to the low numbers of farms tested in the study and the potential confounding effects of vaccination protocols due to problems with these particular diseases on these farms. There was an increased odds ratio for PMWS in herds in which more than 90% of 12-week-old pigs tested positive for PCV2 antibodies (OR = 5.99). The authors suggest that these findings may indicate that pigs infected at earlier stages with PCV2 are more at risk for developing PMWS.

López-Soria S, Segalés, Rose N, Vinãs MJ, Blanchard P, Madec F, Jestin A, Casal J, Domingo M. Preventive Veterinary Medicine 69: 97-107, 2005.